You won’t need a green thumb for this experiment; after all, you’ll be growing mold, not marigolds! By collecting germs from your toes, your pet iguana’s cage, and other icky places, you’ll grow all sorts of goodies in this gloriously gross garden!
What you will need:
- five baby food jars with lids
- two cups of hot water
- one packet of unflavored gelatin
- cotton string
- masking tape
What to do:
1. To make sure that your molds will grow from the bacteria you collect and not from the jar itself, you’ll need to sterilize the jars by rinsing them with hot soapy water. Afterward, pour boiling water into each jar and let the jars stand for a few minutes. Drain the water from jars and let them air-dry. Boil the lids in water for five minutes.
2. Add two cups of water to the gelatin and mix until dissolved. Pour the gelatin mixture into the baby food jars until each jar is half-full, then put the left-over gelatin aside for later use. The gelatin will serve as food for your molds; they grow well on gelatin because of its high protein content.
3. Place a lid on one of the jars and use a marker and masking tape to label it “Control.” (A control serves as a standard of comparison in any science experiment. By being sterile, it’ll let you compare changes happening in your other jars, which will be filled with yucky germs.)
4. Cut four pieces of string (each about 8î long), and dip each string into the leftover gelatin.
5. Now it’s time to get really gross! Drag each gelatin-covered string around in a different area of your house and/or on your body. Try collecting bacteria from your toenails, your cat’s litterbox, your toilet seat, you name it!
6. Place each string into the gelatin solution and label each jar with the place from which you collected germs. Place a lid on each jar.
7. Write down a hypothesis, or educated guess, of which places will grow molds most quickly.
8. Within a week, or even 24 hours, you should have a variety of molds growing in the gelatin solutions.
Colonies of bacteria can be seen growing in all the jars except the one labeled “control.”
Why this happens:
Bacteria are one-celled microscopic organisms that are found just about everywhere–in air, water, soil, and on living things. The gelatin provides a culture medium, or specially-prepared nutritious substance, on which bacteria can grow into a visible colony. Chances are you didn’t find colonies in the jar labeled “control” because you rinsed it with soapy, boiling water (which would kill any germs that had been in the jar). Look back at your hypothesis. Did you correctly predict which places would grow molds most quickly? Why or why not?
For more fascinating findings, you may want to explore new approaches to this experiment; for example, how does temperature affect the growth of bacteria? You can repeat the above experiment and make two of each germ sample from four different locations. Label each pair “warm” and “cold,” then place the “warm” jars in a dark, warm place (like near a radiator) and the “cold” jars in a dark, cool place like a refrigerator. Write down your predictions on where bacteria will grow most quickly, then compare them with what really happens.